FSS - Fixed Satellite Service
DBS - Direct Broadcast Satellite
Both types of satellites use the Ku band frequency but different parts of it in the Americas. FSS uses 11.7-12.2 GHz range, while DBS uses the 12.2-12.7 GHz range. Also, FSS satellites use a less powerful signal than their DBS counterparts. That's why you usually need at least a 30 inch dish to pickup a FSS satellite, while needing only an 18 inch dish for a single DBS satellite.